Physics 207 WebPages - Fall 1999

Problem 3 (Problem 21 in Textbook)

A flywheel completes 40 rev as it slows form an angular speed of 1.5 rad/s to a complete stop.

(a) Assuming uniform acceleration, what is the time required for it to come to rest?

Solution:

Because the rotational acceleration is constant, we can use the kinematics approach. Using an equation from Table 11-1, we obtain the following setup.

(b) What is the angular acceleration?

Solution:

Again, we use another equation from Table 11-1.

(c) How much time is required for it to complete the first 20 of the 40 revolutions?

Solution:

Using the value from part (b) and an equation from Table 11-1, we obtain the following setup.

The quadratic equation here gives two answers; however, it cannot be greater than the answer obtained in part (a). Thus, the other answer, 570 s, is too big.

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